Migrate a .NET test project from Moq 4.21 to NSubstitute 6.2
A tested migration of an xUnit v3 test project on .NET 10 from Moq 4.21.0 to NSubstitute 6.2.0: the full API mapping table, out parameters, events, protected members, partial mocks, and four gotchas that a mechanical find-and-replace walks straight into.